Zend certified PHP/Magento developer

How to run a JS code as soon as a user logs in through checkout. Magento 1.9

Guys I need to run a code as soon as a user logs in through checkout. But I’m not getting it, precisely because it sends a request to “/customer/account/loginPost/” and the return is a refresh to the checkout page.

 public function loginPostAction()
{
    if (!$this->_validateFormKey()) {
        $this->_redirect('*/*/');
        return;
    }

    if ($this->_getSession()->isLoggedIn()) {
        $this->_redirect('*/*/');
        return;
    }

    $session = $this->_getSession();

    if ($this->getRequest()->isPost()) {
        $login = $this->getRequest()->getPost('login');
        $context = $this->getRequest()->getPost('context');

        if (!empty($login['username']) && !empty($login['password'])) {

            try {
                $session->login($login['username'], $login['password']);

                if (!empty($context)) {
                    echo $context;
                }

                if ($session->getCustomer()->getIsJustConfirmed()) {
                    $this->_welcomeCustomer($session->getCustomer(), true);
                }
            } catch (Mage_Core_Exception $e) {
                if (!empty($login['isajax'])) {

                    return;
                }
                switch ($e->getCode()) {
                    case Mage_Customer_Model_Customer::EXCEPTION_EMAIL_NOT_CONFIRMED:
                        $value = $this->_getHelper('customer')->getEmailConfirmationUrl($login['username']);
                        $message = $this->_getHelper('customer')->__('This account is not confirmed. <a href="%s">Click here</a> to resend confirmation email.', $value);
                        break;
                    case Mage_Customer_Model_Customer::EXCEPTION_INVALID_EMAIL_OR_PASSWORD:
                        $message = $e->getMessage();
                        break;
                    default:
                        $message = $e->getMessage();
                }
                $session->addError($message);
                $session->setUsername($login['username']);
            } catch (Exception $e) {
                //Mage::logException($e); // PA DSS violation: this exception log can disclose customer password
            }
        } else {
            $session->addError($this->__('Login and password are required.'));
        }
    }
    if (!empty($login['isajax'])) {
        return;
    } else {
        $this->_loginPostRedirect();
    }
}

I need it to keep running but run a js code “$this->_loginPostRedirect();”

I managed to get the request this way.

 jQuery.ajax({
            url: "<?php echo $this->getUrl('customer/account/loginPost') ?>",
            type: "POST",
            success: function(data) {
                if (data) {
                  
                }

            }

        });

The problem is that it returns the checkout page, and I need to put a parameter inside the if that really confirms that it is the checkout login, and run only on login, not on page refresh.